Background: The most prevalent pro-inflammatory biomarker found in neutrophilic granulocytes is myeloperoxidase enzyme. In order to fight various microbial activities, proinflammatory factors and oxidative stress at the infection site release it from these cells. Several reactive oxygen and nitrogen species are produced as a result of MPO's antimicrobial actions. Aim and objectives: This study aimed to assess the diagnostic value of myeloperoxidase elevation in parenchymal lung disease and airway disease in children. Subjects and methods: This cross-sectional investigation was carried out at the Pediatrics Department of the Suez Canal University Hospitals Faculty of Medicine. 99 patients were split into 3 groups: Group A had 33 patients with pneumonia, group B had 33 patients with bronchiolitis and group C had 33 patients with bronchial asthma in addition to 33 healthy cases as control group. Results: Serum and salivary MPO levels were reliable in the diagnosis of pneumonia, but only serum MPO level can be used to diagnose patients with asthma.  However, serum and salivary MPO levels failed to diagnose patients with bronchiolitis. Also, salivary MPO failed to diagnose patients with asthma. Moreover, serum and salivary MPO levels failed to predict outcome among pneumonia, bronchiolitis and asthma patients. Conclusion: Both serum and salivary myeloperoxidase levels were significantly differed between pneumonia, bronchiolitis, bronchial asthma and control groups, suggesting the potential role of MPO in the diagnosis of parenchymal lung disease and airway disease in pediatrics.